Epithelium

A: Endothelium which is simple squamous epithelium lines the inside of the entire circulatory system.
B: Tunica media is composed of smooth muscle. There is more smooth muscle in the arteries than in the vesins
C: Tunica Adventitia is composed of connective tissue

A: The endothelium is the very thin layer of simple squamous on top of the thin black line which is the internal elastic lamina

B: The tunica media is smooth muscle and is found just beneath the thin black layer that is the internal elastic lamina